Sound reproducing apparatus



y 9 193% n. d. WHELAN- 1,804,295

SOUND I QERRODUCING APPARATUS Filed Dec. 5%, 192

HLs'Attor'ne .atented ay 5, i931 Mam "rArEN OFFEE DOW O. OF SCOTIA,YORK, ASSIGNOR TO GENERAL ELEOTRIO COMPANY, A CORPORATION OF NEW YORKscum) nnrnonocrnearramrus Application filed December 28, 1929. SerialNo. 417,248.

I My invention relates to apparatus for reproducing sound from a filmrecord. Apparatus of this character now in common use employs the Wellknown arrangement comprising an incandescent lamp operated from astorage battery or motor-generator set, an Optical system for projectinga light beam therefrom in a narrow band on the sound record portion ofthe moving film, a photoelectric device behind the film and anamplifying means and a loud speaker connected with the output circuit ofthe photo-electric device. Under certain conditions where such qualitiesin the equipment as lightness, portability, space requirements,simplicity and cost are import-ant considerations as for example inapparatus intended for use in the home or in apparatus intended to beassembled in small compass and to be transported by hand, it becomeshighly desirable to dispense with he storage battery or motorgeneratorset and to operate the lamp from the house or commercial lightingcircuit which also is usually employed in such apparatus to drive thefilm. Such lighting circuits almost invariably supply alternatingcurrent and although the frequency, usually 60 cycles, is too high toproduce any visually perceptible flicker of the lamp, theresultingintensity variations in the light produce an objectionably' loud bum inthe loud speaker unless the amplifyingcharacteristic thereof is modifiedfor the purpose of eliminating the lower range of frequencies. It is theobject of my invention to provide an improved sound reproducingapparatus with which the frequency hum resulting from an alternatingcurrent energization' of the lamp is largely, if not entirely,eliminated without sacrificing the low frequency characteristics of theamplifying and sound reproducing system. Referring to the drawingwherein I have illustrated my invention in a diagrammatic manner, thelamp 1 having the filament 2 is shown connected through the-step-downtrans former 3 to the alternating current line 4;. Light from the lamp 1is focused by the optical system 5 to a narrow beam on the sound recordportion of the film 6 which is caused to move through the beam at auniform speed; Where the film passes through the light beam it isshownby way. of example as supported by the rotatable drum 7 and on thatside of the film opposite the lamp is the photo-electric cell 8 arrangedto receive the light as modulated by the sound record. Con

nected in the usual manner with the output circuit of the photo-electriccell 8 are the translating device 9, shown for example as a loudspeaker. and suitable current amplifying means. The latter I haveillustrated as comprising the two units 10 and 11 which may be of anywell known construction. Connected with the output circuit of thephoto-electric cell 8 is the mechanically resonant filter 12 which inthe form I have'illustrated comprises the core 13 having two lgsprovided with the winding l i shown series-connected in the outputcircuit between the photo-electric cell and the first amplifier unit 10.The armature15- which for example may be constructed of spring steel isshown secured at one end to one leg of the core and is adapted tovibrate freely at .the other end adjacent to the other core leg. -Thearmature is carefully tuned to have 'a natural period of vibration equalto the number of alternations or half waves per second of thealternating current supply circuit 4'. llhe temperature of and hence theradiation from the filament 2 of the lamp undergo periodicvariations-which if the supply has the standard cycle frequency will be120 per second .since each cycle produces two light impulses. Theselight impulses as well as the sound impulsesare transformed into currentimpulses by the photo-electric cell.

Assuming a 60 cycle line frequency, the armature is tuned to makelQOvibrations per second and in so vibrating, the filter greatly increasesthe impedance which it offers to waves having the same frequency. Bythis lamp variations which component is dissipated mechanically in the vbrating element.

In the event that the sound made by the vibrat-ing armature isobjectionable it may be overcome by well known means such as by asuitable damping of the armature or by arranging the filter in a soundproof receptacle. If desired the armature may be resiliently supportedso that thg entire armature vibrates relativeto the core; in any case,the

specific construction of the filter is not essential to my invention.While I have shown the filter arranged between the photo-electric celland the first amplifier ilO it may under certain conditions be founddesirable to arrange it between the two amplifiers or even between thesecond amplifier 11 and the loud speaker.

I have; chosen the particular embodiment described above as illustrativeof my invention and it will be apparent that various modifications maybe made without departing from the spirit and scope of my inventionwhichtmodifications I aim to cover by the appended claims. I

What I claim as new and desire to secure by Letters Patent of theUnitedStates is:

1. An electrical amplifying and sound reproducing system having analternating current supply and having means for eliminating anundesirable frequency, due to said supply comprising a mechanicallyresonant filter provided with an armature tuned for movement in unisonwith said frequency.

2. Sound reproducing apparatus comprising a light source adapted to beenergized by an alternating current, means for passing a sound recordthrough a'narrow beam of light from said source, aphoto-electric devicearranged to receive the light beam modulated by the sound record, atranslating device con- 55 ing a light source adapted to be energized bynected with the output circuit of said photoelectric device, and amechanically resrinant filter connected with said output circuit tunedto the alternation frequency of said current.

3. Sound reproducing apparatus comprising a light source adapted to beenergized by an alternating current, means for passing a sound recordthrough a narrow beam of light from said source, a photo-electricdevicearra'ngedto receive the light beam modulated by the sound record,translating and amplifying devices connected with the output circuit ofsaid photo-electric device and a methereby, said member being tuned tothe frequency of alternation of said current.

5. Sound reproducing apparatus comprising a light source adapted to beenergized v by an alternating current, means for passing a sound recordthrough a narrow beam of light from-said source, a photo-electric devicearranged to receive the light beam modulated by the sound record, anamplifier and a sound producing device connected with the output circuitof said photo-electric device and a filter comprising an electro-magnethaving a winding connected with said circuit and having a vibratoryarmature tuned to the alternation frequency of said current.

6. Sound reproducing apparatus comprising an incandescent lamp havingcircuit connections with a source of alternating current, means forsupporting a moving sound record film, optical means for focusing anarrow beam of light from said lamp on the sound record of the film, aphoto-electric cell arranged behind the film, an amplifier and loudspeaker connected with the output circuit or" the cell and a filter inthe output circuit of the cell comprising a core having a windingthereon and an armature tuned to vibrate in unison with the alternationfrequency of the alternating current.

, In witness .whereof,:1 have hereunto set my hand this 27th day ofDecember, 1929.

DOW O. VVHELAN.

chanically resonant filter connected with said output circuit having avibratory member tuned to the frequency of alternation of said current.v

4. Sound reproducing apparatus comprisan alternating current, meansfor'passing a sound record through a narrowbeam of light from saidsource, a photo-electric device arranged to receive the light beammodulated by the sound record, a sound producing device and an amplifierconnected with the output circuit of said photo-electric device, and afilter having a winding connected with said 5 circuit and a vibratorymember actuated.

